MOLECULAR DESIGN OF A MOLECULAR SYRINGE MIMIC FOR METAL-CATIONS USINGA 1,3-ALTERNATE CALIX[4]ARENE CAVITY

A 1,3-alternate calix[4]arene bearing a nitrogen-containing crown cap at one side and a bis(ethoxyethoxy) group at another side has been syn thesized. H-1 NMR spectroscopic studies showed that Ag+ is bound to th e crown-capped side (log K-ass. = 9.78: CD2Cl2:CD3OD = 4:1 v/v,30 degr ees C), and the dissociation of Ag+ from this cavity is very slow. Whe n the nitrogen atom in the crown ring is protonated with trifluoroacet ic acid, Ag+ is pushed out to the bis(ethoxyethoxy) side through a pi- basic tube of the 1,3-alternate calix[4]arene. The dissociation of the complex from the bis(ethoxyethoxy) side occurs relatively fast. On th e other hand, when the nitrogen . H+ in the crown ring is deprotonated with Li2CO3 and diazabicycloundecene, Ag+ is sucked back to the crown -capped side through the pi-basic tube. These chemically-switchable ac tions well imitate the function of a ''syringe'', using the pi-basic t ube as a pipette and the crown ring as a rubber cap. We believe that t his prototype of a ''molecular syringe'' is a novel molecular architec ture for the action of metal cations.